Frame of chair backrest



FIG. 1 is a perspective view of frame of chair backrest showing my new design.

FIG. 2 is a front view thereof.

FIG. 3 is a rear view thereof.

FIG. 4 is a left end view thereof.

FIG. 5 is a right end view thereof.

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a frame of chair backrest, as shown and described. 